Control Of Doubly-Fed Wind Power System Based On Sliding Mode Theory

In today’s wind power generation system,because the speed of the generator in the VSCF wind power system can change with the change of the wind speed and maintain at the optimal speed at all times,it is favored because of its high energy conversion efficiency.Doubly-fed wind power generation system is a kind of VSCF wind power generation system.Due to the increasing single unit capacity of the current doubly-fed generator(Double Fed Induction Generator,DFIG),it will produce a certain impact current between the doubly-fed generator and the power grid,which will affect the stability of the power grid,which can not be ignored.After successful grid connection,it is necessary to change the control strategy and adopt the control strategy of maximum wind energy tracking.Starting from these two aspects,this paper studies the grid connection and maximum wind energy tracking of doubly-fed wind power generation system in turn.(1)Firstly,the research background and significance of the paper are introduced,and then the development status of wind power at home and abroad is analyzed.It leads to the no-load grid connection and maximum wind energy tracking control of the doubly-fed wind power system studied in this paper.The structure of the doubly-fed wind power generation system is analyzed,and the core equipment of the system,the wind turbine and the doubly-fed generator,are studied to prepare for the design of the follow-up system controller.(2)The mathematical model of DFIG no-load operation is derived,Firstly,an integral sliding mode controller is designed to be used in the no-load grid-connected control system of doubly-fed wind power generation system.The simulation results show that the integral sliding mode control has better speed and less steady-state error than PI control.Due to the characteristics of sliding mode control,chattering occurs when the system reaches the sliding mode surface.The symbolic function sgn is replaced by fal function,and then the switching gain of integral sliding mode controller is adjusted in real time by RBF neural network.Finally,the proposed algorithm is simulated under the conditions of grid voltage stability and grid voltage fluctuation.The results show that the chattering phenomenon of the improved integral sliding mode controller is weakened than before.The robustness of the system is stronger and the steady state error is smaller.(3)Variable resistance is used to simulate the change of generator speed to simplify the rotor-side converter of doubly-fed wind power system.The stable operation of the grid-side converter is the premise of controlling the rotor-side converter to achieve maximum wind energy tracking.Firstly,a sliding mode controller is designed for the grid-side converter control system,aiming at the lack of passive anti-jamming robustness of sliding mode control.Furthermore,a sliding mode auto-disturbance rejection compound controller is designed,and the extended state observer in the controller is used to observe and compensate the system interference.The simulation results show that the grid-side converter under sliding mode ADRC can maintain the stability of DC-side voltage and ensure the two-way flow of power.The simulation is carried out under the condition of stable operation and disturbance,and the control effect is compared with that of sliding mode control and PI control.The simulation results show that the sliding mode ADRC designed in this paper increases the anti-jamming ability and rapidity of the system compared with the other two controllers.(4)The maximum wind energy tracking of doubly-fed wind power generation system can be realized by controlling the rotor-side converter.Firstly,a double closed-loop rotor side converter control system is designed,and a sliding mode controller is designed to replace the PI controller for the speed outer loop.The simulation results show that the sliding mode controller can complete VSCF power generation and power decoupling control of doubly-fed wind power generation system,that is,maximum wind energy tracking.Aiming at the fluctuation and overshoot of DFIG speed waveform,the fractional order theory and grey prediction theory are introduced respectively,and the speed outer loop grey prediction fractional sliding mode controller is designed.The characteristic of fractional calculus slowly attenuating with time is used to reduce the speed fluctuation,and grey prediction combined with sliding mode control is used to realize prior prediction,advance control and improve the performance of the system.Finally,the simulation results show that the algorithm reduces the fluctuation of generator speed and realizes the speed non-overshoot operation.